1. Field of the Invention
Embodiments of the invention generally relate to a gas distribution plate assembly and method for distributing gas in a processing chamber.
2. Description of the Background Art
Liquid crystal displays or flat panels are commonly used for active matrix displays such as computer and television monitors. Plasma enhanced chemical vapor deposition (PECVD) is generally employed to deposit thin films on a substrate such as a transparent substrate for flat panel display or semiconductor wafer. PECVD is generally accomplished by introducing a precursor gas or gas mixture into a vacuum chamber that contains a substrate. The precursor gas or gas mixture is typically directed downwardly through a distribution plate situated near the top of the chamber. The precursor gas or gas mixture in the chamber is energized (e.g., excited) into a plasma by applying radio frequency (RF) power to the chamber from one or more RF sources coupled to the chamber. The excited gas or gas mixture reacts to form a layer of material on a surface of the substrate that is positioned on a temperature controlled substrate support. Volatile by-products produced during the reaction are pumped from the chamber through an exhaust system.
Flat panels processed by PECVD techniques are typically large, often exceeding 370 mm×470 mm. Large area substrates approaching and exceeding 4 square meters are envisioned in the near future. Gas distribution plates (or gas diffuser plates) utilized to provide uniform process gas flow over flat panels are relatively large in size, particularly as compared to gas distribution plates utilized for 200 mm and 300 mm semiconductor wafer processing.
As the size of substrates continues to grow in the TFT-LCD industry, film thickness and film property uniformity control for large area plasma-enhanced chemical vapor deposition (PECVD) becomes an issue. TFT is one type of flat panel display. The difference of deposition rate and/or film property, such as film stress, between the center and the edge of the substrate becomes significant.
Therefore, there is a need for an improved gas distribution plate assembly that improves the uniformities of film deposition thickness and film properties.